Module 3: Weather, Loading, and Performance

What is the troposphere?

The lowest layer in the atmosphere, which is characterized as a region where, in general, temperature decreases with altitude

What is the ABL?

Atmospheric Boundary Layer; the lowest layer of the troposphere that’s strongly influenced by the Earth’s surface

What is turbulence?

Temporary fluctuations, or gustiness, that are superimposed on the sustained wind

How is thermal turbulence created?

Through the uneven heating of the Earth’s surface, which causes pockets of warm air to rise

What three aspects influence the intensity of thermal turbulence?

1) Surface type: Materials such as asphalt, rock, and sand heat up faster than grass or water, creating stronger temperature contrasts
2) Time of day: Turbulence typically peaks during midday and afternoon when solar radiation is strongest
3) Atmospheric conditions: Higher temperatures and unstable air masses can intensify updrafts/downdrafts

How is mechanical turbulence created?

By wind shear, which are abrupt changes in the speed or direction of the flow, brought about by the force of the drag

What three aspects influence the intensity of mechanical turbulence?

1) Differences in wind speed and direction: Stronger winds that flow in opposite horizontal directions generally create more severe turbulence
2) Surface roughness and density: Irregular terrain or areas with dense obstacles or obstructions like urban environments cause greater disruption than smooth surfaces like flat oceans

3) Air stability: Unstable air allows eddies to grow larger and more chaotic, while stable air causes them to dissipate more slowly

Thermal turbulence can be considered ______ while mechanical turbulence can be considered ______

1) Vertical turbulence
2) Horizontal turbulence

When should stronger wind speeds be expected?

During daytime hours and with an increase in altitude

How are stratus clouds characterized?

Gray and layered in appearance, typically covering the entire sky

How are cumulus clouds characterized?

Distinct, puffy clouds that are more vertically developed, often appearing like cotton balls in the sky with flat bases

______ is associated with precipitation that fall from stratus or cumulus clouds

Nimbus

What are the six sky descriptions that are used based on the fraction of the sky covered by clouds?

1) Clear (CLR)
2) Few clouds (FEW)
3) Scattered (SCT) or partly cloudly
4) Broken (BKN) or cloudy
5) Overcast (OVC)
6) Sky obscured

When is fog characterized as dense?

When the restriction limits the visibility to less than one-quarter mile

How does radiation fog occur?

By the cooling of air adjacent to the ground

When does radiation fog occur?

Often on clear, relatively calm nights, when the ground emits more radiation than it absorbs

What is advection?

The horizontal movement of air

How does advection fog occur?

If the air is cooled below its dew point

How does evaporation/mixing fog occur?

When an air mass becomes saturated by the addition of water vapor

The most common form of evaporation fog is called ______

Steam fog